Mr Harrison "actually grabbed the second diver who went past him," Mr Chamberlain said, adding that the diver concerned got quite a fright.

"This changed the whole nature of the operation to a rescue operation."

Decompression

But even after Mr Harrison had been found, he still faced a complex process to bring him out safely.

Having been at such depth for so many hours, he needed time in a decompression chamber to normalise his body pressure.

Christine Cridge, a medical director at the Diving Diseases Research Centre (DDRC), advised the rescue team during this process.

"It's a situation I've not come across before," she told the BBC's Newsday programme.

"After a certain amount of time at pressure, nitrogen will dissolve into the tissues. If he'd ascended directly from 30m to the sea surface..... it's likely he'd have had a cardiac arrest, or at best, serious neurological issues.

Mr Harrison describes his story as a "miracle", but he also told Reuters: "When I am at home sometimes it feels like the bed I am sleeping in is sinking. I think I'm still in the sea again. I jump up and I scream."

Jan Messchendorp, general manager of West African Ventures said in a statement: "We are very grateful for the survival of Mr Harrison. Our thoughts continue to be with the families of the rest of the crew."

He added that the search and rescue operation has now been stopped for safety reasons.